In the real time processing of digital data, the problem of determining whether or not the current digital data has been previously observed and processed, is often encountered. For example, if a radio receiver, used for a radar system, is being employed to observe and identify various radar transmitters, it is often the case that a radar pulse that is first received is often followed soon thereafter by a second pulse, which was originated by the reflection of the first pulse from some physical object. It is useful to identify the second pulse as a reflection of the first pulse, so as to avoid redundant and erroneous processing thereof. If such is accomplished, a substantial reduction in the receiver's suppression of duplicate data reports is realized. Normally, the radar system comprises a host system digital processor, which analyzes the received digital output, and is relatively busy because of its sorting and correlating of received signals from the transmitting source for identification purposes. If the receiver is also generating redundant reports, which do not correspond to actual signal activity, the host system digital processor is unnecessarily burdened, and may not even be capable of performing its needed sorting and correlating operations.
The common technique for identifying a second pulse as being a reflection of a first pulse, is to measure the RF frequency of the first pulse, and then look for the same RF frequency measurement within a group of near term or subsequent pulses. There are, however, errors present in the measurement of the RF frequency and therefore, the reflected pulse may exhibit a similar, but not necessarily identical, RF frequency measurement. Furthermore, there may be more than one reflective pulse, so that the process of measuring the RF frequency has to consider multiple events. Because of the speed or response time of the radio receiver and because of the fact that there may well be multiple radar transmitters being simultaneously observed by the radio receiver, reflective pulses may not even be contiguous with the first pulse, but rather, there may be many intervening unrelated pulses received that may also have associated reflective signals and all of which require the same RF frequency measurement identification process. This measurement identification process may be unable to handle all such possibilities.
Prior art devices and techniques have addressed the redundant digital data problem by primarily using an exact match technique, whereby the current digital data is compared exactly to the previous data to provide identification therebetween. Whereas these exact comparisons yielded proper results, they did not provide the solution for detecting similar data. The detection of similar data usually required the employment of relatively complicated software techniques that demanded relatively long processing times to yield adequate results. Further, attempts have been made to assert similarity between data by a simple truncation method for handling the data. For example, if the measured data exhibits a 12 bit resolution but an accuracy of 10 bits is only needed, then a comparison is made only on the 10 most significant bits (MSB's). Such a comparison does not always yield adequate results. In particular, consider the following 10 bit digital data word: 01 1111 1111, and then compare it to the next adjacent word that is increased by one (1) bit: 10 0000 0000. A comparison between the first 10 bit digital word and the second 10 bit digital word reveals that requiring an exact comparison, even on the reduced (10 bits) resolution, fails to associate a 1 bit difference therebetween and, therefore, this technique fails to detect similarity between data words. It is desired that means be provided to not only detect exact data between previous and currently received digital data words, but also detect similar data between previous and presently received digital data words.
It is, therefore, a primary object of the present invention to provide for a circuit arrangement for associating two digital words occurring randomly in a serial stream of digital words and determine if any one thereof is a similar or exact word, relative to previously received digital words, so as to avoid the erroneous processing of the exact and similar words.
It is a further object of the present invention to provide a method for detecting redundant exact or similar words occurring between two digital words that are randomly present in a serial stream of digital words.
It is a still further object of the present invention to provide a circuit arrangement, as well as a method of use thereof, for determining redundant, exact and similar words received by a radio receiver used within a radar system and having both multi-path blanking and leading edge trigger modes of operation.
It is another object of the present invention to provide a circuit arrangement and a method of use thereof that are easily altered so as to accommodate different parameters of a radar system.
Other objects of the present invention, as well as the advantages thereof over existing and prior art forms, which will be apparent in view of the following detailed description, are accomplished by the means hereinafter described and claimed.